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John |
#17
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"Ordinary" PMTs, of which the 931 and similar ones like the 1P28
and even the ones with the photocathode on the front glass, are not permanently damaged by room light, and the 931 and 1P28 won't be by even straight sunlight. That's turned off of course. Far red multialkali ones might be by the sun, but I've never seen it happen, and I've used hundreds of these things. However!! They can "charge up" and take hours, or for the red ones even a week or two, to fully recover their original low light dark current performance. Just let them sit in the dark for an hour before using if you're fussy. |
#18
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Here's the "official" answer: Has anyone ever had a window break in their car? No matter how much you vacuum or clean you almost always find a glass shard that mystically appears! RCA was always big on this prospect and most plumbicons would come shipped with a gimbal to keep the tube UPRIGHT and NOT FACE DOWN for fear that GLASS OR METAL particles (not dust) that may have lodged in the unit could fall down and hit the TARGET. (NO PUN INTENDED) These tubes were all 100% hand made and no matter how hard you clean the assemblies, debris can be present. Iconoscopes usually were never a victim of this unless they were broken or dropped in some way and also were too rugged to be bothered by this phenomenon. Most all image orthicons were labeled to not store or ship face down.
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julian Last edited by julianburke; 01-24-2015 at 04:24 PM. |
#19
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Re: the 931A being sensitive to fluorescent room light.
The early B&K Analyst flying spot scanner CRT produces lots of blue light and a good amount of ultraviolet as well. The 931A is the photomultiplier tube used in these old B&Ks because it is most sensitive to blue light. The B&K was running full tilt to produce the B&W TV test pattern image and even after many years the test signal is still quite contrasty and visually noise free. Just trying to reconcile the "damage from room light" and the use of the 931A in the B&K Analyst that continues to work well even now. |
#20
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Audiokarma |
#21
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This may be what we were seeing. Still it's curious that the two manufacturers were different.
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#22
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Very nice display, those tubes look "off the assembly line" brand new! Reading through the replies asking whether the Iconoscope is still any good, I personally think if there's no whiteness around the getters then it's still under vacuum and would likely be good for use, my RCA 1846 Iconoscope tube I recently got working in my homemade camera is outputting a picture. I was advised with vintage tubes that have been doormat for decades to fire up the tube heater at 3V for 2 hours and then 5V for 1 hour to rejuvinate them and so I did that with my 1846 and it's working! Those not aware of my homemade Iconoscope camera here is the link to my thread on it http://videokarma.org/showthread.php?t=263849 .
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AUSSIE AUSSIE AUSSIE!!!!! OI OI OI!!!!! |
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